Attempts have been made to use a light-weighted magnesium alloy as a material for manufacturing members of an exterior casing of a miniaturized portable electronic equipment such as a mobile communication equipment or a notebook-type personal computer, a material for manufacturing members of a large-sized casing such as a traveling suitcase or a document accommodating attaché case, a material for manufacturing automobile-use members such as a hood, a trunk lid, doors or fenders and the like. However, magnesium alloy exhibits poor formability and hence, it is extremely difficult to perform press-forming with a high degree of forming. As a method for forming such hard-to-form magnesium alloy by drawing, there have been proposed several methods which heat magnesium alloy to a recrystallization temperature region at the time of press-forming including a method which performs press-forming by drawing after heating a die, a punch, and a wrinkle pressing member of a drawing forming device to an approximately 150 to 400° C. (see patent document 1, for example), and a magnesium-alloy-made hard-case manufacturing method which heats a die, a punch and a blank holder, and heats magnesium to a recrystallization temperature region by way of these press-forming tools, and forms a magnesium blank into a box shape by hot deep drawing while inducing an annealing effect in which magnesium is easily recrystallized, softened and deformed by heating (see patent document 2, for example).
Further, there has been also proposed a method which uses a lubricant for facilitating forming. For example, there have been proposed a method which forms a super-hard thin layer such as titanium nitride or diamond-like carbon on a surface of a press mold by coating (see patent document 3, for example), and a method which performs press-forming using a plastic forming oil for magnesium alloy or aluminum alloy containing biodegradable oil and fat, a rust-proofing lubricant, an extreme-pressure additive, an organic zinc compound, and an organic molybdenum based compound (see patent document 4, for example). However, even when magnesium alloy is press-formed by heating magnesium alloy, by using the lubricant, or by heating magnesium alloy while using the lubricant, abrasions are liable to be formed on a surface of magnesium alloy which comes into contact with a tool at the time of forming. Accordingly, magnesium alloy cannot be used in applications where aesthetic surface appearance is required.
To prevent the formation of abrasions on the surface of magnesium alloy at the time of press-forming, there have been proposed a method which performs plastic forming by mounting a plate made of pure magnesium, pure aluminum or a resin softer than a magnesium alloy material on a surface of at least one of a punch and a die (see patent document 5, for example), and a method which performs press forming of magnesium alloy at a high temperature by mounting a fluororesin film sheet on upper and lower surfaces of a heated magnesium thin plate as a heat insulation material (see patent document 6, for example). However, in these methods, the soft plate made of pure magnesium, pure aluminum or a resin or the fluororesin film sheet used as the heat insulation material must be exchanged in use for every forming and hence, these methods are not favorable for the continuous production. Further, since the fluororesin film sheet is particularly expensive, a press-formed body obtained by these methods inevitably becomes disadvantageous in terms of cost.
As prior art literatures relevant to the present invention, the following are named.    Patent Document 1: JP-A-2003-290843    Patent Document 2: JP-A-2002-254115    Patent Document 3: JP-A-2003-154418    Patent Document 4: JP-A-2003-105364    Patent Document 5: JP-A-2001-300643    Patent Document 6: JP-A-6-328155